Next.js: Styles disappear during HMR

[Peeja]

Steps to Reproduce

1. pnpm create next-app --example with-goober with-goober-app
2. cd with-goober-app
3. pnpm run dev
4. Open page. Notice h1 is black.
5. Refresh. Notice h1 is orange.
6. Change one of the strings in page.tsx. Notice h1 is black again.
7. Refresh. Notice h1 is orange again.

Expected: The h1 should always be orange (tomato).
Actual: The h1 is black on first load after dev server startup and after HMR.

When the h1 is black, it's because all of the CSS is missing. You can even console.log({css}) and see { css: '' } when the CSS disappears, and { css: '.go…' } when it returns.